1. Field of Invention
The present invention relates to a data-line driver circuit. More particularly, the present invention relates to a data-line circuit for a current-programmed electro-luminescence display device,
2. Description of Related Art
Electro-luminescence (EL) device is activated through a current drove method either in passive matrix scheme or active matrix scheme. Especially in the active scheme, the charge is held on a capacitor and applied to the pixels of EL device through a transistor driver circuit. A simplest and essential driver circuit of an active-matrix electro-luminescence display device is illustrated in FIG. 1. In FIG. 1, transistor 102 is called a switching thin film transistor (switching TFT) and transistor 104 modulates the current for driving a light-emission element 108 in response to a signal voltage of a storage capacitor 106, so the transistor 104 is called a driving TFT. The signal voltage stored in the storage capacitor 106 is refreshed per frame time.
Nonetheless, the method of utilizing voltages to drive directly the driving TFT 104 as in the foregoing description would generate different light intensities by the same driving voltage due to every driving TFT having different characters. Therefore, a method of utilizing currents to drive the driving TFT 104 is generally used to adjust the threshold voltage and the mobility of the driving TFT 104.
However, there is a disadvantage of an electro-luminescence display device driven by currents. Data currents are generally provided by data lines, so the quantity of current sources must be equal to the quantity of data lines. In other words, many data lines and current sources are required to satisfy the demands for large size and high resolution in modern electro-luminescence display devices. Sony Corp. therefore has provided a current latch circuit to decrease the quantity of current sources, as illustrated in FIG. 2.
In FIG. 2, the current latch circuit includes a circuit 202, a circuit 204, a circuit 206, a circuit 212, a circuit 214, a circuit 216, a shift register (SR) 208, a shift register 218, an enabling means 209, an enabling means 219 and a pixel group 220. The circuit 202 and circuit 212 are in charge of red pixels of the pixel group 220, the circuit 204 and circuit 214 are in charge of green pixels of the pixel group 220, and the circuit 206 and circuit 216 are in charge of blue pixels of the pixel group 220. The pixel group 220 includes a plurality of pixels; a scanning line switches these pixels for writing data currents. The shift register 208 and the enabling means 209 control a first circuit group 201; the first circuit group 201 includes the circuit 202, the circuit 204, and the circuit 206. The shift register 218 and the enabling means 219 control a second circuit group 211; the first circuit group 211 includes the circuit 212, the circuit 214, and the circuit 216.
The input data procedures of the current latch circuit in FIG. 2 is described as follows. The shift register 208 sequentially writes a data current Idata into the circuits of the first circuit group 201, when the data current Idata is sent to the current latch circuit. After finishing the foregoing writing procedure of the first circuit group, the shift register 218 is switched to write sequentially the subsequent data current Idata into the circuits of the second circuit group 211. Meanwhile, the enabling means 209 instructs the first circuit group 201 to send the data current Idata stored therein to corresponding pixels of the pixel group 220. Similarly, after finishing the writing procedure of the second circuit group 211, the shift register 208 is switched again to write the data current Idata into the first circuit group 201, and, at the same time, the enabling means 219 instructs the second circuit group 211 to send the data current Idata stored therein to corresponding pixels of the pixel group 220,
The first circuit group 201 and the second circuit group 211 take turns receiving and then sending the data current. While data current is being written into one, the other is in charge of sending another data current to the pixel group. And after both of them have finished these procedures, they interchange their functions, thus repeatedly receiving and sending out the data currents.
This current latch circuit can substantially decrease the quantity of current sources, but each circuit groups and each shift register thereof must be controlled by external control signal (not shown) because this current latch circuit is based on two circuit groups interchanging. Disadvantages of the conventional system include too many external control signal lines and poor quality of the display device because two individual circuit groups interfere somewhat with the data currents.